Question

I have a sequence of xml elements like this:

<addr>via roma</addr>
<addr>via milano</addr>
<addr>via napoli</addr>
...

and I want to check if there is a sequence of addresses containing the same consecutive address 3 or more times, like:

<addr> via napoli</addr>
<addr>via roma</addr>
<addr>via roma</addr>
<addr>via roma</addr>
<addr>via milano</addr>
....

This input sequence of xml elements is the result of xquery. I think I should use the fn:matches() function but I can’t write the regular expression that matches this sequence.

Answer 1

This query (and Xpath 3.0 expression) produces true() exactly when the sequence $seq contains $n or more consecutive items having the same string value:

    boolean($seq
              [some $i in 1 to count($seq) -($n -1)
                 satisfies
                    not(distinct-values(subsequence($seq, $i, $n))[2])
              ]
             )

So, in this specific case:

let $n := 3,
    $seq := /*/addr
 return
        boolean($seq
                  [some $i in 1 to count($seq) -($n -1)
                     satisfies
                        not(distinct-values(subsequence($seq, $i, $n))[2])
                  ]
                 )

produces

true